(1) Field of the Invention
This invention is directed to condensation products and methods for the preparation of condensation products of phenol, urea, and formaldehyde which provide cellular plastic compositions useful as insulation material.
(2) Description of the Prior Art
Heretofore, foamed materials derived from condensates of a phenol and formaldehyde have been prepared by mixing a liquid phenol-formaldehyde resin, a blowing agent, optionally a surfactant, and then a curing (i.e., hardening) agent, such as a strong acid, and applying heat to volatilise the blowing agent and harden the resin.
Such compositions and the methods of their preparation posed obvious disadvantages, particularly if large sections of rigid, foamed condensates were required. Big ovens or a large number of infra-red heaters were required to supply heat evenly over the whole surface. Since the foams possessed good heat-insulating properties, it was very difficult to supply heat to the interior of a large block of the foamed condensate. Irregular heating resulted in a non-uniform foam which was unsuitable for the purpose for which it was intended and which was structurally weak. Since external heaters or ovens are required to obtain a satisfactory rate of hardening, ("on-site") preparation of foams was difficult, or even impossible, and this was a further disadvantage of such compositions and methods.
In attempts to overcome these drawbacks, other substances have been included in the resin mixture which react exothermically with the curing agent and thus reduce or remove the need for applying heat to cure the resin. Solid substances which have been so used include phosphorus pentoxide, barium oxide, and calcium carbonate. However, such exothermically-reacting substances are sometimes unpleasant to handle on an industrial scale, the foams contain inert materials which add to the weight of the product, but serve no useful purpose, and since the unfoamed starting mixtures contain solids, it is difficult to obtain uniform suspensions, which will give uniform foams. This is especially true if a continuous method of foaming is employed. Alternatively, as shwon by U.S. Pat. No. 3,692,706, liquids have been added which react exothermically to form a polymer under the influence of the curing agent. However, even the use of this expedient does not solve the major drawback of all these systems which is that they all require a chemical blowing agent. In other words, the phenol-formaldehyde resins cannot be foamed, placed, and set by simple mechanical agitation and pumping.
While insulation materials based on condensates of urea and formaldehyde have been foamed, placed and set by simple mechanical agitation and pumping, such materials have unsatisfactory to poor chemcial and physical properties for many thermal and acoustical insulation uses for which such condensates are intended. For example, such condensates have poor compressive strength, tensile strength, shear strength, and their water solubility is too high for many insulation uses for which they are intended in the building industry. In addition, their flame spread characteristic is higher than desirable for many applications in the building industry where safety is an important feature.
Mixtures of phenol-formaldehyde and urea-formaldehyde condensates and certain urea-phenol-formaldehyde condensates are known in the art, see U.S. Pat. Nos. 3,077,458 and 3,549,473, but these materials have characteristics restricting their use to liquid films or binders.